In the past, normal lines of an object have been calculated from polarized images having a plurality of different polarization directions. For example, NPLs 1 and 2 describe a normal line calculation that is performed by applying polarized images having a plurality of different polarization directions to a model equation.
Additionally, for example, an object is recognized by using polarized images. PTL 1, for example, describes object illumination that is performed by disposing illumination means such that the resulting illumination light is p-polarized light with respect to a predetermined reference plane. PTL 1 also describes object identification that is achieved based on light intensity measurement results by separating light reflected from the reference plane into s-polarized light and p-polarized light, measuring the light intensity of each polarization component, and measuring the light intensity while moving a measurement target along the reference plane.
Further, the normal lines are used as a user interface. According to PTL 2, for example, an operation of a target corresponding to a hand and a forearm is detected to recognize a motion similar to a natural motion of the human body that is performed to turn a page. The normal lines of a target plane corresponding to the palm of the hand are used to detect the motion. Meanwhile, the target is detected by extracting the distance distribution and outline of a distance image.